1. Field of the Invention
The invention relates to a thin-walled circular-shaped metal structure and a method of fabricating the same, and more particularly to such a metal structure usable as a photosensitive drum or a fixing roller in an electrophotographic printer or copier, and a method of fabricating the same.
2. Description of the Related Art
For instance, in accordance with Japanese Unexamined Patent Publication No. 10-10893, a film of which a photosensitive drum or a fixing drum used in a conventional electrophotographic printer and copier is formed is composed generally of organic material such as polyimide or metal as inorganic material, such as iron, aluminum, stainless steel and nickel.
Such a film generally has a practical thickness in the range of 0.03 to 0.20 mm. However, such a practical thickness can be accomplished only by a film composed of polyimide or nickel. For instance, a nickel film having such a thickness can be fabricated by electrocasting.
It is generally said that a fixation section consumes about 80% of power to be totally consumed in an electrophotographic printer or copier. In addition, power consumption depends highly on material of which a fixing roller or a fixing film is composed.
For instance, if a fixing roller or film is composed of polyimide, which is organic material having a thermal conductivity 1/510 to 1/40 smaller than a thermal conductivity of the above-mentioned iron, aluminum, stainless steel or nickel, it would be necessary to heat a fixing roller or film much time until the fixing roller or film become workable. A period of time in which a fixing roller or film is heated is a time in which a user has to wait after a printer or copier has been turned on until the printer or copier becomes workable.
It is desired in business that a printer or copier becomes workable as soon as possible, and hence, a fixing roller or film has to be preheated even when the printer or copier is not in use, resulting in increase in power consumption.
On the other hand, if a fixing roller or film is composed of nickel having a thermal conductivity 210 times greater than a thermal conductivity of polyimide, it would be possible to shorten a time for heating the fixing roller or film until the fixing roller or film becomes workable. As a result, it is no longer necessary to preheat a fixing roller or film, and hence, a printer or copier including the fixing roller or film composed of nickel becomes workable immediately when the printer or copier is turned on.
As mentioned above, power consumption in a printer or copier can be reduced by using a nickel film as a fixing film. However, a conventional method of fabricating a nickel film is accompanied with problems as follows.
As mentioned earlier, a nickel film having a thickness of 0.03 to 0.20 mm is fabricated by electrocasting. That is, such a nickel film is fabricated by precipitating nickel ions by electrolysis. Hence, the thus fabricated nickel film has such columnar crystal structure, and resultingly, has a shortcoming that the nickel film is weak to mechanically repeated stress.
In addition, in accordance with a fatigue test, a nickel film has a lifetime in the range of a couple of tens thousand rotation to a couple of millions rotation. There is much dispersion in lifetime of a nickel film.
In particular, a nickel film fabricated by electrocasting shows remarkable thermal embrittlement when heated to a temperature over 200 degrees centigrade. Hence, a nickel film fabricated by electrocasting is not suitable as a fixing film.
Though ions can be readily precipitated out of pure metal by electrocasting, it is almost impossible to precipitate ions out of an alloy such as stainless steel.
As another method of fabricating a metal cylindrical film, there has been suggested a method including the steps of rounding a thin film having a thickness in the range of 0.03 to 0.20 mm, and welding the thus rounded film into a cylinder-shaped film. According to this method, any metal may be used for fabricating a metal cylindrical film.
However, this method is accompanied with problems of shortage in a mechanical strength and non-uniformity in a shape of a cylinder, due to a bead treatment at a welded portion, and further due to defect in a welded portion with respect to a metal structure. In addition, since a metal cylindrical film is fabricated in the method by splicing thin films to each other, skill and much time are required for fabricating a metal cylindrical film, resulting in increase in cost and absence of mass-productivity. Hence, the method is not put to practical use yet.